1. Field
The present disclosure relates generally to video encoding and, more specifically, to techniques for content adaptive video frame slicing and non-uniform access unit coding for improved coding efficiency.
2. Background
In all of the current video compression standards, coded representations of video frames or the so called video access units, VAUs, comprise slices as the next lower layer in coding hierarchy. Slice layer allows a functional grouping of (the data of) an integer number of macroblocks in the video frame, fundamentally serving as a resynchronization unit within the coded representation of the frame. In order to serve as proper resynchronization points, all predictive coding schemes/dependencies such as intra-prediction (based on neighboring pixels) and motion vector prediction, are disabled across all slice boundaries.
Until H.264 (and excluding the optional ‘Annex K: Slice Structured Mode’ Rectangular Slices Submode of H.263+), prior video compression standards such as H.261, MPEG-1, MPEG-2/H.262, H.263, and MPEG-4, supported a slice structure essentially consisting of an integer number of consecutive (in raster scan order) macroblocks, with minor differences in how slice sizes were constrained.
The H.264 standard introduced the concept of ‘slice groups’ which enables the partitioning of the macroblocks of a frame into slice groups and into slices within slice groups, in a totally arbitrary manner and, therefore not constrained by having to be consecutive in raster scan order. This arbitrary decomposition is described through the so called ‘slice group maps’ which get transmitted to the decoder in addition to the compressed data of the frame. This provision is known as Flexible Macroblock Ordering (FMO).
There is therefore a need for techniques for content adaptive video frame slicing and non-uniform access unit coding for improved coding efficiency.